The present invention relates to a steering apparatus for a vehicle and to an industrial vehicle.
A full-electric steering apparatus is disclosed in Japanese Laid-Open Patent Publication No. Hei 7-206399, as a kind of steering apparatus in a vehicle such as an industrial vehicle. An order picking truck in this application comprises a controller. The controller inputs the rotation angle of a steering wheel from a potentiometer, and inputs a steered angle of a steered wheel from another potentiometer. The controller calculates deviation of voltages detected by both potentiometers, and outputs a driving voltage that corresponds to the deviation to a steering motor. The steered wheel is turned by the driving force of the steering motor to by an angle that corresponds to the rotated angle of the steering wheel. Since the steering wheel is not mechanically coupled to the steered wheel, the steering wheel can be rotated even if the steered wheel reaches a limit of steering.
The known steering apparatuses include a full-hydraulic power steering apparatus that turns the steered wheel by supplying a steering cylinder with oil the amount of which corresponds to the amount of steering wheel operation.
FIG. 6(a) shows such a steering apparatus, which is provided with a stopper 52 for a supporting member supporting a steered wheel 51. The apparatus of FIG. 6(a) also has stopper blocks 53a and 53b in positions that correspond to steering limits (end positions) of a left turn and a right turn of the steered wheel 51. As shown in FIG. 6(b), when the stopper 52 contacts the stopper block 53b, the steered wheel 51 is stopped at the end position of the right turn. When the stopper 52 contacts the stopper block 53a, the steered wheel 51 is stopped at the end position of the left turn.
However, in the steering apparatus shown in FIG. 6(a), when the stopper 52 contacts the stopper block 53a or the stopper block 53b, an impact is made on, for example, a gear part that conveys the driving force of the steering motor to the steered wheel 51. The gear part also receives the driving force of the steering motor. This may break the gear part. It is therefore necessary to process the gear part to make it stronger against impacts, which requires much labor in manufacturing the gear parts. Further, impacts on the gear part generate unpleasant noise.
In a power steering apparatus disclosed in Japanese Laid-Open Patent Publication No. Hei 10-157637, turning motion of the steered wheel 51 is decelerated as the steered wheel 51 approaches any of the steering limits. This reduces impacts made when the stopper 52 contacts the stopper blocks 53a and 53b. 
However, although impacts and the load of the steering motor are somewhat reduced, the stopper 52 contacts the stopper blocks 53a, 53b. The gear part therefore still receives the impacts and the load. Since the turning speed of the steered wheel 51 is decelerated near the steering limits, the responsiveness of the steered wheel 51 to the steering wheel operation is lowered near the steering limits.
It is a first objective of the present invention to provide a steering apparatus and an industrial vehicle that stop turning motion of a steered wheel at end positions without causing the stopper of the steered wheel to contact stopper blocks, and are capable of holding the steered wheel at the end positions.
It is a second objective of the present invention to provide a steering apparatus and an industrial vehicle that improve responsiveness of the steered wheel to operation of a steering wheel without reducing the turning speed of the steered wheel near the ends.
To achieve the foregoing objective, the present invention provides a steering apparatus for a vehicle. The steering apparatus includes a manipulator, a steered wheel, a first detector, a driving device, a second detector and a controller. The steered wheel is steered in a steered range, which is between two predetermined end positions. The first detector detects operation of the manipulator and outputs a signal representing the detection result. The driving device generates a driving force to steer the steered wheel. The second detector detects at least one of two states of the steered wheel and outputs a signal representing the detection result. In one of the states, the steered wheel is at either of the end positions. In the other state, the steered wheel is deviated from either of the end positions. The controller controls the driving device. The controller causes the driving device to steer the steered wheel in accordance with the signal from the first detector. When the steered wheel reaches either one of the end positions, the controller causes the driving device to stop steering motion of the steered wheel based on the signal from the second detector and to hold the steered wheel at the end position.
The present invention also provides a forklift having a steering apparatus. The steering apparatus includes a manipulator, a steered wheel, a first detector, a driving device, a second detector and a controller. The steered wheel is steered in a steered range, which is between two predetermined end positions. The first detector detects operation of the manipulator and outputs a signal representing the detection result. The driving device generates a driving force to steer the steered wheel. The second detector detects at least one of two states of the steered wheel and outputs a signal representing the detection result. In one of the states, the steered wheel is at either of the end positions. In the other state, the steered wheel is deviated from either of the end positions. The controller controls the driving device. The controller causes the driving device to steer the steered wheel in accordance with the signal from the first detector. When the steered wheel reaches either one of the end positions, the controller causes the driving device to stop steering motion of the steered wheel based on the signal from the second detector and to hold the steered wheel at the end position.
Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.